1. Field of the Invention
The present invention relates to an imaging control arrangement for use in imaging systems.
2. Description of the Prior Art
Many imaging techniques exist, particularly sonic systems.
The `Pencil Beam` method, uses a single transducer (or an array functioning as a single transducer) sends a narrow pulsed beam in a certain direction. The transducer then functions as a receiver; received echoes are used to modulate the deflection (A scan) or brightness (B scan) of an oscilloscope trace. Mechanical movement of the transducer may be linked to displacements in position and angle of the oscilloscope trace, in order to produce cross-sectional images (tomographs) coplanar with the direction of the sonic beam. This technique is widely employed in medicine, in underwater sonar, and in non-destructive testing.
In Holographic methods, objects are irradiated by a continuous sound beam; the transmitted or reflected beam from the object is then caused to interfere either with another sound beam or an electronic simulation thereof, forming a hologram on the surface of a liquid or upon a photographic film. This in turn is viewed by coherent light to recover the image information.
There are Sokolov camera methods in which a transmitted or reflected sound beam falls on a piezo-electric plate forming the end face of a TV camera tube. The received sound amplitude at a spot on the tube may be read out by scanning the back face of the piezo-electric plate with an electron beam. This amplitude signal is then directly transferred to another TV screen.
In film or liquid crystal methods, the response of photographic film, or a film of a liquid crystal material directly sensitive to ultrasound, is used to form the image.
What are termed synthetic aperture methods exist. Here the object medium is irradiated in turn by a matrix of transmitters, and echo information is recorded at a matrix of receivers. This information is then reassembled numerically by a computer to form a "pulse hologram", which may be converted to an acoustic image by further computation, or by viewing the pulsed hologram in coherent light.
In Timoshin's method, a single pulse transmitter is used in conjunction with an array of receivers, whose echo-time spectrum is recorded. This total echo information is then used to reconstruct the image of a desired focal plane in object space by a process called D-conversion. D-conversion is a computational technique which may be applied after all information has been received. D-conversion considers a certain object plane element, and integrates all information which could have been reflected by that element to appear in the time trace of any receiver. An image of the object plane is built up by repeating this process element by element.
In focussed systems, the object is irradiated with a beam of sound (usually continuous), and the reflections are focussed by an acoustic lens on an image plane. This may be viewed either by a Sokolov camera or by a matrix of small piezo electric elements.
A recent development is direct ultrasonic visualisation which uses pulsed sonic irradiation, with dual acoustic lenses to form a three dimensional sonic image in a photo elastic medium. This medium is then illuminated by pulsed light, using crossed polaroids to detect areas of strain at sonic image foci.